Liquid crystal display (LCD) devices have been used in a variety of applications, including calculators, watches, color televisions and computer monitors. Use of LCD devices has been accelerated owing to the advancement of techniques for manufacturing LCD devices, particularly active matrix type devices that utilize thin film transistors (TFTs) to drive pixel elements of the device.
A conventional liquid crystal panel typically includes a pair of transparent glass substrates that are arranged in parallel to define a narrow gap therebetween that is filled with a liquid crystal material. A plurality of pixel electrodes typically are disposed in a matrix on an inner surface of one of the transparent glass substrates, and a plurality of common electrodes corresponding to the pixel electrodes are arranged on the inner surface of the other substrate of the two transparent glass substrates. A liquid crystal cell is defined by opposing pixel and common electrodes. Images are displayed by controlling light transmission through the cell according to a voltage applied to the electrode pair.
In a conventional active matrix LCD device, a plurality of parallel gate lines are formed on one substrate, transverse to a plurality of data lines. A plurality of pixel electrodes is disposed on a corresponding plurality of pixels regions defined by the gate and data lines. A respective thin-film transistor (TFT) is formed on a respective one of the pixel regions, and drives the pixel electrode formed thereon.
FIG. 1A is a plan view of a conventional liquid crystal panel. Gate lines G1-Gm extend transverse to data lines S1-S3n, defining pixel regions on which pixel electrodes P and thin film transistors TFT are formed. The TFTs for driving a column of pixel electrodes typically have first controlled electrodes connected to a data line extending along a side of the column, and second controlled electrodes connected to respective pixel electrodes in the column. Voltages are applied from the data lines S1-S3n to the pixel electrodes P by selectively driving gate electrodes of the TFTs, which are connected to the gate lines G1-Gm.
Applying voltages having the same polarity to a liquid crystal cell can cause an electrochemical change in the pixel electrode and the common electrode due to precipitation of ionic impurities from the liquid crystal material. This change can significantly reduce display sensitivity and brightness. Accordingly, it is generally desirable to periodically invert the polarity of the voltage applied to the liquid crystal cell in order to prevent this phenomenon.
As illustrated in FIGS. 1B-1C, a conventional dot inversion driving technique involves applying data line voltages that have different polarities to adjacent pixel electrodes, for example, by driving alternating pixel elements with negative (hatched) and positive (no hatching) voltages. Typically, the polarity of the voltages applied to a given pixel electrode is inverted at each frame, as illustrated by FIGS. 1B and FIG. 1C, which illustrate inversion between a first frame (FIG. 1B) and a second frame (FIG. 1C). FIG. 2 illustrates how a data line voltage applied during a frame F inverts with each line period H with respect to a 5V signal used to drive the common electrode of the cell. The data line is driven by voltages from 0V to 10V to provide the appropriate polarity for the pixel electrodes connected thereto. The specified voltage values are used only as examples -0V, 5V and 10V. In actuality, the voltage values depend on panel characteristics.
Although the above-mentioned conventional dot-inversion driving technique may improve display characteristics, such a technique may be disadvantageous because the polarity of the data line voltage is inverted after each horizontal line period. Switching operations typically are required to achieve the inversion, which can lead to undesirably high power consumption. Furthermore, each voltage inversion may require a significant amount of time and may lead to insufficient charging of the cell after each inversion, resulting in poor display performance.